[PATCH v2] tcp: Add listening address to SYN flood message

[Jamie Bainbridge <jamie.bainbridge@gmail.com>]

The SYN flood message prints the listening port number, but with many
processes bound to the same port on different IPs, it's impossible to
tell which socket is the problem.

Add the listen IP address to the SYN flood message in the "IP.port"
format like most other tools (eg: tcpdump).

Each protcol's "any" address and a host address now look like:

 Possible SYN flooding on port 0.0.0.0.9001.
 Possible SYN flooding on port 127.0.0.1.9001.
 Possible SYN flooding on port ::.9001.
 Possible SYN flooding on port fc00::1.9001.

Signed-off-by: Jamie Bainbridge <jamie.bainbridge@gmail.com>
---
v2: Place IS_ENABLED() inside if condition c/o Andrew Lunn.
    Change port printf to unsigned c/o Stephen Hemminger.
    Remove long and unhelpful "Check SNMP counters" c/o Stephen.
    Use IP.port format c/o Eric Dumazet.
---
 net/ipv4/tcp_input.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 0640453fce54b6daae0861d948f3db075830daf6..5b156dfc13b3d45c20e4fe6a45af7c42f39b2c66 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -6831,9 +6831,17 @@ static bool tcp_syn_flood_action(const struct sock *sk, const char *proto)
 		__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPREQQFULLDROP);
 
 	if (!queue->synflood_warned && syncookies != 2 &&
-	    xchg(&queue->synflood_warned, 1) == 0)
-		net_info_ratelimited("%s: Possible SYN flooding on port %d. %s.  Check SNMP counters.\n",
-				     proto, sk->sk_num, msg);
+	    xchg(&queue->synflood_warned, 1) == 0) {
+		if (IS_ENABLED(CONFIG_IPV6) && sk->sk_family == AF_INET6) {
+			net_info_ratelimited("%s: Possible SYN flooding on port %pI6c.%u. %s.\n",
+					proto, &sk->sk_v6_rcv_saddr,
+					sk->sk_num, msg);
+		} else {
+			net_info_ratelimited("%s: Possible SYN flooding on port %pI4.%u. %s.\n",
+					proto, &sk->sk_rcv_saddr,
+					sk->sk_num, msg);
+		}
+	}
 
 	return want_cookie;
 }
-- 
2.38.1